This invention relates to printing mechanisms and, in particular, to wiping printheads of an inkjet printing mechanism to clean residual ink and contaminants off of the printheads.
An inkjet printer includes a printing assembly having a printhead, or printheads, to deposit ink onto a print media, such as paper. A printhead has an orifice plate that is formed with nozzles through which ink drops are xe2x80x9cfiredxe2x80x9d, or otherwise ejected, onto the print media to form an image, such as text or a picture. The ink drops dry, or are heated to dry, on the print media shortly after deposition to form the printed image.
There are various types of inkjet printheads including, for example, thermal inkjet printheads and piezoelectric inkjet printheads. For a thermal inkjet printhead, ink droplets are ejected from individual nozzles by localized heating with a heating element located at individual nozzles. An electric current is applied to a heating element to heat it up which causes a small volume of ink to be rapidly heated and vaporized. Once vaporized, the ink is ejected through the nozzle. A driver circuit is coupled to individual heating elements to provide the energy pulses and thereby controllably deposit ink drops from associated individual nozzles. The drivers are responsive to character generators and other image forming circuitry to energize selected nozzles of a printhead for forming images on the print media.
During printing, ink tends to build up at the nozzle orifices of a printhead. This build-up of residual ink can be caused by ink droplets that are not completely ejected from a nozzle, excess ink at the orifice that is not fully vaporized, or ink spatterings that reflect from the print media when the ink is ejected. The small nozzle orifices of a printhead are also susceptible to clogging by quick drying ink, dust particles and paper fibers, and from solids within the ink. Partially or completely blocked nozzles can result in either missing or misdirected ink drops being deposited onto the print media, either of which impairs printing and degrades the print quality.
The printing assembly typically includes a service station having wipers to clean and preserve the functionality of the printheads. The service station includes a wiper, or wipers, for wiping a printhead to remove ink residue and other contaminants that have been deposited or collected on the printhead surface and over the nozzle openings in the printhead surface. A service station can also include a cap, or capping mechanism, which covers a printhead when the printer is not printing to prevent the ink in the nozzles from drying, and to prevent contaminants from collecting in and over the nozzles.
Although a service station provides wipers, or a wiper system, that substantially cleans and removes residual ink and contaminants from printheads, conventional wiping techniques can cause the residual ink and contaminants removed from a printhead to be xe2x80x9cflickedxe2x80x9d or otherwise splattered and deposited in an undesirable location that will impair or degrade printing. For example, when a wiper travels across a printhead to remove the residual ink, the wiper is under tension to maintain contact with the printhead and effectively clean the printhead. When the wiper reaches an end of the printhead, the wiper travels off or past the printhead, which causes the wiper contact tension with the printhead to be released. Releasing the tension on the wiper causes any collected residual ink and contaminants to be flicked off of the wiper which can be deposited in undesirable locations, such as on the print media, or on an adjacent printhead.
Accordingly, there is an ever-present need to provide a wiping technique that effectively cleans a printhead while preventing residual ink and contaminants removed from the printhead being deposited in locations that will impair or degrade a desired print quality.
A print unit, such as an inkjet printing mechanism, includes a print module having one or more printheads to deposit an imaging medium, such as ink, on a print media. The print unit also includes a wiper assembly having one or more wipers that correspond to the one or more printheads, such that when the wiper assembly and the print module are positioned in proximity to service the printheads, the wipers clean the printheads of ink residue and contaminants.
A wiper cleans, or wipes, a printhead when the wiper and the printhead are in contact and when the wiper and/or the printhead is moved relative to the other in a first direction. For example, the wiper can move in a direction that is parallel to a longitudinal axis of the printhead, or the printhead can move in the parallel direction relative to the wiper. A contact tension between the wiper and the printhead holds, or otherwise seats the wiper against the printhead to facilitate cleaning the printhead.
The wiper and the printhead also move relative to each other in at least a second direction to release the contact tension between the wiper and the printhead. For example, the wiper can move in a perpendicular direction relative to the printhead, or the printhead can move in the perpendicular direction relative to the wiper. When the wiper and/or the printhead move in both the first direction and the second direction, the wiper for example, moves along an arc path defined by the first and second directions such that the wiper is moved down and away from the printhead. The wiper is moved along the arc path to controllably release the wiper contact tension and prevent ink residue on the wiper from being flicked, or otherwise deposited in a location that will impair or degrade a desired print quality.